Why Dark Knight's Flying 'Bat' Wouldn't Fly

When the Dark Knight rises to defend Gotham once more, he literally takes to the skies in a flying vehicle known simply as the Bat. The new nonlethal weapon in Batman's arsenal can hover like a helicopter and pull off aerial maneuvers worthy of "Top Gun" fighter jets — a combination that may seem almost too good to be true.

That amazing spectacle should come as no surprise in a Hollywood film about a billionaire superhero with access to top-secret military technology. But making the Bat fly in today's reality would prove a lot trickier, said Mitchell Burnside Clapp, a program manager for the U.S. military's Defense Advanced Research Projects Agency (DARPA).

"The problem with a vehicle like the Bat is that it's going to have to generate enough thrust to hold itself off the ground," Burnside Clapp said. "The main thrust appears to come from the belly rotor while the other devices seem to be applied more to maneuvering."

Burnside Clapp looks to the future of aircraft technology as manager for DARPA's Disc-Rotor Compound Helicopter program. He previously served as an Air Force Reserve instructor at the U.S. Air Force Test Pilot School and worked at several private aerospace companies. In this case, he has also seen "The Dark Knight Rises" (Warning: plot spoilers ahead; no character spoilers).

Making the Bat fly

Downward thrust from the Bat's belly rotor must at least equal the weight of the Bat to achieve the hover effect, Burnside Clapp explained. Helicopters create such lift by having long rotor blades extending well beyond the main aircraft body — the blade sections close to the main rotor hub do not create much lift because they don't move very fast relative to the air.

But helicopter lift also depends on accelerating air downward through their spinning rotor blades. That becomes a problem if the rotor sits underneath an aircraft such as the Bat (although Lucius Fox, Batman's gadgets master in the Christopher Nolan film trilogy, mutters something about solving air recirculation issues in the Bat's design).

Putting the main rotor beneath the Bat also leads to some stability problems — "think of the problem of balancing a broomstick on your palm" to get an idea, Burnside Clapp told InnovationNewsDaily. By comparison, rotors act as a restoring force for stability when they sit on top of helicopters. [V-22 Osprey: Controversial Dream Machine]

Assuming the Bat weighs about as much as modern helicopters, the Bat's rotor would still need to have "enough air to push a several thousand pound vehicle upwards," Burnside Clapp said. Such force would easily knock a standing person down, which would have changed certain "Dark Knight Rises" scenes in a fairly dramatic fashion.

Leaping the technology gap

Still, some technologies could make hovering vertical takeoff and landing (VTOL) aircraft work in the confined urban canyons of Batman's Gotham City. Shrouded rotors distributed around the Bat vehicle could prevent the downwash from flattening everyone around it, Burnside Clapp said.

Enough power can make almost anything fly (maybe even a prohibitively expensive flying aircraft carrier). Helicopters represent a power-efficient way of providing lift, followed by the less efficient "vectored thrust" aircraft such as the F-35 Joint Strike Fighter.

By comparison, the Bat's unusual design would lead to huge power demands — but perhaps not unsolvable demands, according to the technological leaps of fancy in "The Dark Knight Rises."

"The Bat, in the film, would need an unbelievable amount of power," Burnside Clapp said. "Now if you had a fusion reactor big enough to power a city that was small enough that you could carry it around in a medium truck, then …"